Conventionally, for example, as described in JP-A No. 2009-144916, a tube joint has been proposed, which is able to be firmly coupled so as not to leak fluid passing inside a tube.
In this tube joint, in the case in which a tube is attached to an end part of a cylindrical joint body to screw a coupling nut onto the joint body, a fixation ring is disposed between the coupling nut and the joint body. Then, when the coupling nut is screwed onto the joint body, the tube is tightened from inside the tube by the joint body and from outside the tube by the fixation ring pressed by the coupling nut.
In this tube joint, since the above configuration has been employed, when the coupling nut is screwed onto the joint body, the coupling nut rotates about the tube while the fixation ring does not rotate about the tube. Therefore, it is described that this tube joint is able to prevent an annular flaw from being made on the outer surface of the tube due to the friction between the outer surface and the fixation ring and the tube from being cut due to the friction between the outer surface and the fixation ring.